Intercontinental undersea communication cables may be used to transmit high speed digital signals over low loss fiber optics. Repeaters are needed at various intervals to amplify and restore attenuated light signals. The repeaters are electronic devices which require power. The repeaters are typically a plurality of light emitting diodes (LEDs) which are used to excite laser amplifiers embedded in the individual optical fibers. More complex repeaters, which receive the light pulses, convert the light pulses to electrical signals and retransmit optical pulses, may also be needed due to the accumulated dispersion of the very long undersea communication cables.
To deliver power to the repeaters, high voltage, low current DC power sources e.g., ±15 kV, 1 A, are placed at each end of the undersea communication cable. This power is carried to all the repeaters by a single communication power conductor. The repeaters are connected in series such that source current flows through the repeaters. The voltage to sea ground varies significantly along the cable, from a very high positive voltage at the positive end, falling at each repeater, turning negative, and falling to a maximum negative voltage at the negative end. The repeaters are electrically isolated from sea ground and are powered by current flowing from one end of the cable to the other without regard to the voltage to sea ground.
There is often a need to create a branch from the undersea communication cable so communication between more than two points may obtained without requiring completely separate cables. Powering the repeaters in a branch can be problematic since the main power conductor cannot be branched and the relative voltage to sea water at any particular point is unknown variable or not at all defined. In addition, it may be desired to supply power to nearby external load which may have an arbitrary and dynamically changing resistance or power, such as undersea devices, equipment, and the like, not related to the typical main function of the undersea communication cable.